1. Field of the Invention
The present invention generally relates to data backup and data storage such as storage of data on tape drives and, more particularly, data storage systems adapted to provide efficient and high-quality data protection during the process of transferring data files from one storage device or system to another storage device or system (e.g., transferring data from disk storage to tape storage).
2. Relevant Background
For decades, magnetic tape data storage has offered cost and storage density advantages over many other data storage technologies including disk storage. A typical medium to large-sized data center will deploy both tape and disk storage to complement each other, with the tape storage often used for backup and archival data storage. Due to the increased need for securely storing data for long periods of time and due to the low cost of tape, it is likely that tape-based data storage will continue to be utilized and its use will only expand for the foreseeable future. Briefly, magnetic tape data storage uses digital recording on to magnetic tape to store digital information, and the tape is packaged in cartridges (i.e., the storage media or simply “media”). The device that performs writing and reading of data is a tape drive, and tape drives are often installed within robotic tape libraries, which may be quite large and hold thousands of cartridges to provide a tremendous amount of data storage (e.g., each tape may hold several terabytes of uncompressed data).
An ongoing challenge, though, for the data storage industry is how to provide data protection during the transfer of data (e.g., large data files) from disk storage (i.e., a first data storage device) to tape storage (i.e., a second data storage device). Specifically, it is important to verify that a file or object has not changed during the transfer processes. This fundamental goal of digital preservation can be attained by establishing and checking the “fixity” or stability of the digital content. Fixity is the property of a digital file or object being fixed or unchanged during the transfer processes such as during archiving processes from disk to tape storage, and it can be thought of as bit-level integrity of the data as fixity information offers evidence that one set of bits is identical to another (i.e., that the archived data matches the data on the first storage device).
Transferring data from one storage system to another is a potential point at which digital content can be damaged. It is, therefore, critical to check the fixity of the content whenever it is moved such as when it is archived from a user system to an archive data storage system. Some storage systems have been designed to have fixity built into the storage system so that data is regularly checked after transfer. For example, some data storage systems provide checksums on tape, such as per-block checksums. However, checking fixity of archived data has typically required that the data has to be read back from the tape drive (or tape library) to the host application, and such a read back operation can be very time consuming for large data archiving processes.
Hence, there remains a need for improved methods of checking fixity of transferred data (e.g., of archived data). Preferably, such methods could be built into the data storage system and would enhance transfer operations such as by reducing or even eliminating the need for reading back archived data to a host application. Avoidance of the read back operation is desirable because doing fixity checks increases the usage of the media and of the mechanical devices that read and handle the media, and, for some media, usage may be a factor contributing to the projected failure rate of the media (e.g., a tape cartridge). Further, performing a fixity check can slow other ongoing processes such as archiving or accessing archived data in a tape library or other data storage device, and, as a result, it is desirable to provide ways to check fixity that require less resources to complete.